The present invention is generally directed to a method and peptide for regulating cellular activity, and more particularly to the identification and use of various peptides derived from vaccinia virus A52R protein that have biological effects by inhibiting or enhancing cellular activity, and particularly toll-like receptors (TLR) induced cytokine secretion in a cell.
The innate immune system, involved in both the detection and control of infection, recognizes conserved motifs from pathogens termed pathogen-associated molecular patterns (PAMPs) (References 1 and 2). Toll-like receptors (TLRs) recognize PAMPs, and their interaction triggers a series of intracellular signaling events that culminates in expression of cell-surface molecules, secretion of pro-inflammatory cytokines and induction of acquired immunity (References 2–9). TLRs are characterized by an extracellular leucine-rich repeat motif and an intracellular Toll/IL-1 receptor (TIR) domain. Pathogens are detected by the innate immune system, with recognition of the bacterial PAMPs LPS, CpG DNA, flagellin, and peptidoglycan mediated by TLR4, TLR9, TLR5, and TLR2 respectively (References 4 and 10–13). Recognition of viral infections are mediated primarily by TLR3 in response to viral dsRNA (Reference 14). Cell activation in response to different PAMPs involves a number of intracellular molecules common to all TLRs, including MyD88, members of the IL-1 receptor-associated kinase (IRAK) proteins, TNF receptor associated factor (TRAF6), and NF-κB (Reference 1).
Vaccinia virus, a member of the poxvirus family, is a DNA virus that has been demonstrated to encode immunomodulatory proteins (References 15–18). One of these proteins, A52R, has been shown to inhibit NF-κB activation following initiation of the TIR signaling cascade (References 15 and 18). Recent studies have demonstrated that A52R inhibits TIR signaling and contributes to the virulence of vaccinia virus. Inhibition of TIR signaling by A52R is mediated by binding of the protein to both TRAF6 and IRAK2 (Reference 18).
The present invention is directed to the identification and characterization of a peptide, derived from the A52R protein, that significantly inhibits in vitro cytokine production in response to both bacterial and viral PAMPs. This peptide has characteristics consistent with a reagent that inhibits intracellular signaling triggered by TLR activation. Cytokine secretion induced by non-TLR stimulation was not inhibited by the peptide. The in vivo activity of this peptide was demonstrated by dramatically reducing middle ear inflammation in mice injected with heat-inactivated Streptococcus pneumoniae (S. pneumoniae). This peptide may have application in the treatment of this and other inflammatory conditions that result from ongoing TLR activation. In addition, we have also identified three distinct A52R peptides that inhibit cytokine secretion and five other distinct peptides that enhance cytokine secretion.